1. Field of the Invention
The invention relates to quaternary ammonium salt antimicrobial compositions and methods for treating bacterial infestations. More specifically, the invention relates to mycobactericidal and tuberculocidal compositions comprising quaternary ammonium salts and glycol ethers.
2. Description of the Related Art
Although many virucidal, bactericidal, sporicidal, and fungicidal compositions are known, none is currently available that provides highly efficacious elimination of mycobacteria while furnishing low toxicity, no odor, non-flammability, low skin irritation and no staining upon contact with a surface. Mycobacterium tuberculosis is an organism refractory to treatment by most bactericidal compounds. Its trilaminar cell wall, composed of 60% lipid, peptidoglycan, arabinoglycan, trehalose 6,6' dimycolate, sulfates and mycosides, accounts for the unusual properties of the organism: (a) relative impermeability to stains, (b) acid fastness, and (c) unusual resistance to killing by acid or alkali.
A popular class of compounds used for control of M. tuberculosis are the aldehydes. The preferred aldehyde is glutaraldehyde, which is believed to mediate its cidal action by forming radicals that are able to penetrate the protective cell wall. Glutaraldehyde is an alkylating agent and thus is capable of reacting chemically with sulfhydryl, hydroxyl, and carboxyl groups of proteins. Often these glutaraldehydic formulations include an anionic surfactant that helps penetration of the aldehyde radical by solubilizing the cell membrane through formation of surfactant-lipid-protein complexes. There are several drawbacks to glutaraldehyde in chemical disinfectant usage. They are expensive and can only be diluted to a 0.5% solution or 2.0% if alkaline. They are considered relatively toxic at 0.5% and toxic at 2.0% in handling. They cause severe dermatitis and are allergenic. They have been shown to be unreliable in killing M. tuberculosis. Aldehydes have a strong odor and their vapors are extremely irritating to mucous membranes. The shelf life, once these compounds are mixed is not greater than thirty days for the popular alkaline forms.
Alcohols are known to possess low-level broad spectrum germicidal activity. Ethanol, benzyl alcohol, and isopropanol are currently used in disinfecting compounds effective against M. tuberculosis. Isopropanol, at a concentration of greater than 50% by weight, is the preferred alcohol. Alcohols work by denaturing and precipitating proteins of the microorganism. Alcohols have very low vapor pressures and consequently are quite flammable. Ethyl alcohol is effective against mycobacteria only in concentrations exceeding 50% and thus is a hazard in any bactericidal composition since its flash point is less than 100.degree. F. Isopropanol is less a concern with respect to flammability, but with government regulations concerning volatile organic compounds (VOCs), its use in bactericidal formulations is problematic.
Phenols are widely used for bactericidal action. Highly efficacious, phenols work by precipitating structural and enzymatic proteins thus inactivating the cellular machinery and ultimately leading to cell death. Phenolics used in the formulation of mycobactericidal compositions include ortho phenyl phenol, paratertiary amyl phenol, and benzyl chlorophenol. Phenols have a strong characteristic odor and are quite toxic. Even recently developed phenols which have high molecular weights, have a pungent odor, and, although less toxic than phenol itself, their level of toxicity is still a concern. With increasing molecular weight comes decreasing solubility, and compounds such as paratertiary amylphenol are relatively insoluble in water.
Compositions containing iodophors have been used against mycobacteria. Iodophors have a pervasive iodine smell and will stain any surface with which they come in contact.
Quaternary ammonium salt formulations have been used as disinfectants for many years and these formulations have broad spectrum antimicrobial activity. Although formulations containing higher concentrations of quaternary ammonium salts are known to be effective against certain gram positive and gram negative bacteria, these formulations do not display any tuberculocidal activity.